1. Field of the Invention
The present disclosure relates to stem cell proliferation. More particularly, the disclosed invention relates to the proliferation of limbal epithelial stem cells (LSCs) or hair follicle stem cells (HFSCs).
2. Description of Related Art
Stem cells are associated with the formation, repair, and maintenance of tissues during embryogenesis and injuries and aging in the adults. Stem cells are unique in their self-renewal capacity and differentiation potential. The capacity of self-renewal enables these stem cells to make more copies thereof, whereas differentiation potential allows them to differentiate into multiple or all the germ lineages. These properties are collectively defined as the “stemness” of stem cells.
Mammalian stems cells are broadly categorized into embryonic stem cells and adult stem cells. Embryonic stem cells are derived from the inner cell mass of blastocysts which is formed in the early embryogenesis of mammals. These embryonic stem cells are totipotent, which means they may give rise to all the tissues of a complete organism. Embryonic stem cells can be maintained in culture as undifferentiated cell lines or induced to differentiate into many different lineages, and therefore, they have been widely used in fields of molecular biology and medicine. However, one drawback of maintaining embryonic stem cells in culture is their tendency to differentiate spontaneously and thereby lose their proliferation capacity over time. Many tissues in adult animals have been shown to contain reservoirs of stem cells, which are called “adult stem cells.” Adult stem cells, in comparison with to embryonic stem cells, have a more restricted differentiation capacity, and are usually lineage-specific. These adult stems cells are often associated with the repair and maintenance of tissues. For example, bone marrow stem cells may migrate to various tissues after injuries, while tissue stem cells located outside the bone marrow may repair the tissues in which they reside.
Limbus anatomically locates between cornea and sclera at ocular surface. The basal layer of limbal epithelium is enriched with a special cell population, named limbal epithelial stem cells (LSCs). The cornea is a stratified squamous epithelium with a rapid turnover property that maintains corneal transparency and visual acuity. The renewal of corneal epithelium is supported by the transient amplifying cells (TACs) who are generated by asymmetric division of LSCs. In addition, LSCs are normally slow cycling cells, but activated by corneal wounding that enable corneal damage repaired.
Partial or total loss or dysfunction of LSCs (clinical termed LSC deficiency) leads to corneal neovascularization, recurrent erosions, stromal scarring, ulceration, thereby causing vision loss. LSC deficiency may arise following injuries including chemical or thermal burns and through diseases such as aniridia, chronic infection (e.g., trachoma), mycotic keratitis, and Stevens Johnson syndrome. Currently, transplantation of the ex vivo expanded limbal epithelial sheet has become the most widely used therapy for LSC deficiency. This therapeutic approach generally involves placing a small limbal biopsy removed from either the patient or a donor on transplantable carriers such as denuded human amniotic membrane to support limbal cells migrating out from the biopsy and outgrowth to form a limbal-like epithelial sheet. In addition, enzymatically isolating the limbal cells from limbal tissue and their expansion by suspension culture systems contributes to decrease the LSCs spontaneously differentiation. The failure of limbal transplantation is often arising from the depletion of LSCs in culture. Accordingly, it is desirable to effectively expand the quantity of LSCs in vitro or ex vivo before the transplantation.
Adult mammalian epidermis consists of the hair follicles (HFs), the sebaceous glands (SGs), and the interfollicular epidermis. The homeostasis of each of these three epithelial compartments is supported by their own stem cell (SC) population. Hair follicle stem cells (HFSCs) reside in the hair follicle bulge; they are multipotent and have the capacity to give rise to all epidermal lineages. HFSCs are predominantly responsible for reconstituted HFs during homeostasis rather than responsible for the formation of epidermis. However, after skin wounding, HFSCs contribute to interfollicular epidermal repair. Yet, the in vivo proliferation of HFSCs following the injuries is not fast enough, and may slowdown the wound healing process. Moreover, in the event of large amount of skin loss, such as those resulted from infection, surgical excision, and burn, there may be insufficient available HFSCs to participate in wound healing.
In view of the foregoing, there exists a need in the art to provide a method of promoting the proliferation of stem cells, which in turn may promote wound healing.